Various non-limiting embodiments of the present disclosure relate to photochromic materials comprising a reactive substituent. Other non-limiting embodiments of the present disclosure relate to photochromic articles, compositions, and methods of making the photochromic articles, wherein the photochromic articles and compositions comprise the photochromic materials described herein.
Many conventional photochromic materials, such as, for example, photochromic naphthopyrans, can undergo a transformation from one state to another in response to the absorption of electromagnetic radiation. For example, many conventional photochromic materials are capable of transforming between a first “clear” or “bleached” ground state and a second “colored” activated state in response to the absorption of certain wavelengths of electromagnetic radiation (or “actinic radiation”). As used herein the term “actinic radiation” refers to electromagnetic radiation that is capable of causing a photochromic material to transform from one form or state to another. The photochromic material may then revert back to the clear ground state in response to thermal energy in the absence of actinic radiation. Photochromic articles and compositions that contain one or more photochromic materials, for example photochromic lenses for eyewear applications, generally display clear and colored states that correspond to the photochromic material(s) that they contain. Thus, for example, eyewear lenses that contain photochromic materials can transform from a clear state to a colored state upon exposure to actinic radiation, such as certain wavelengths found in sunlight, and can revert back to the clear state in the absence of such radiation.
When utilized in photochromic articles and compositions, conventional photochromic materials are typically incorporated into a host polymer matrix by one of imbibing, blending and/or bonding. For example, one or more photochromic materials may be intermixed with a polymeric material or precursor thereof, and thereafter the photochromic composition may be formed into the photochromic article or, alternatively, the photochromic composition may be coated on a surface of an optical element as a thin film or layer. As used herein, the term “photochromic composition” refers to a photochromic material in combination with one or more other material, which may or may not be a photochromic material. Alternatively, the photochromic material may be imbibed into a pre-formed article or coating.
In certain circumstances it may be desirable to modify the compatibility of the photochromic material with the host polymer into which it is incorporated. For example, by making the photochromic material more compatible with the host polymer, it is less likely that the combination will demonstrate cloudiness or haze due to phase separation or migration of the photochromic material in the host polymer. In addition, compatibilized photochromic materials may be more soluble in the host polymer and/or more uniformly distributed throughout the polymer matrix. Further, by modifying the compatibility of a photochromic material with a host polymer, other properties of the photochromic composition, such as, but not limited to, fade and/or activation rate, saturated optical density, molar absorptivity or molar extinction coefficient, and activated color, may also be effected. Modifications to such properties may be done, for example, to match the same properties of complementary photochromic materials or to enable the use of such compounds in hydrophilic or hydrophobic coating compositions, thin films or in rigid to flexible plastic matrices.
One approach to modifying the compatibility of a photochromic material with a host polymer is to attach a polymerizable to the photochromic material via a polyalkoxylated linking group, for example, a polyethylene glycol, a polypropylene glycol, and/or a polybutylene glycol linking group. One potential limitation of utilizing polyalkoxylated linking groups is the degree of purity of the resultant photochromic material that can be readily achieved. For example, commercially available polyglycols that may be incorporated into the linking groups of these photochromic materials may comprise mixtures of glycol chains possessing differing numbers of glycol units within each chain. Incorporation of these commercially available polyglycols into the photochromic material may lead to mixtures of compounds differing in chain lengths and molecular weights. This may lead to difficulty in purification, since one cannot readily separate out the desired photochromic materials in these mixtures.
Further, polyalkoxylated linking groups may comprise long chains containing multiple ether oxygen functionalities, which are inherently hydrophilic. While this may present certain desirable traits with regard to compatibility with the host polymer, linking groups with differing hydrophilicities, including linking groups that may be hydrophobic or, alternatively, linking groups of shorter length, may provide for different interactions with the host polymer and the resultant photochromic article.
Accordingly, for some applications it may be desirable to develop photochromic materials that may be incorporated into a variety of host polymers and which may comprise one or more reactive substituents having polarities (i.e. hydrophilicities or lipophilicities) that may more closely match the polarities of the host polymer. In other applications, it may be desirable to develop photochromic materials comprising one or more reactive substituent having polarities that do not match the polarities of the host polymers. In addition, it may be advantageous to develop photochromic materials comprising reactive substituents of uniform composition/molecular weight that can be readily purified, such as, by crystallization, chromatography, or other methods of purification known to one skilled in the art.